The invention relates to the field of encoding program signals to provide compressed digital signals for the program.
The invention relates to an encoding device for encoding a signal, the signal representing a program of a predefined duration, and the encoding device comprising a compression unit for compressing the signal to digital data, and a system controller for controlling the compression unit for influencing the bit rate of the digital data for fitting the program in a data space which is available for the program depending on a remaining part of the data space and a remaining part of the duration established during encoding.
The invention further relates to a recording device for recording a signal on an information carrier, the signal representing a program of a predefined duration, the information carrier having a vacant data space available for recording the program, and the device including recording apparatus for recording a digital bit stream on the information carrier and apparatus for establishing the predefined duration.
The invention further relates to a method of encoding a signal that represents a program of a predefined duration, the signal being converted by a compression process into digital data with a bit rate influenced for fitting the program in a vacant data space which is available for the program, in which method a remaining part of the vacant memory space and a remaining part of the duration are determined during the encoding process and the bit rate is influenced by settings of the compression process depending on the remaining part of the vacant data space and the remaining part of the duration.
The invention further relates to an encoded signal obtained by implementing the method.
Such an encoding device, recording device, method and encoded signal are known from EP-A 0584991. This document discloses a system for encoding video information in digital data for recording a video program having a known duration (such as a film) on a disc, such as a high density optical disc, for example, the so-termed DVD (Digital Video Disc). For this purpose, the system includes a an MPEG like video compression unit arranged for motion compensation, DCT (Discrete Cosine Transform), quantization and variable length coding, as is customary for MPEG. The controller of the compression unit is arranged for controlling the encoding of the video program so as to fit the program within an available data space on the disc. The data space available for storage on the disc is filled by attuning the bitrate of the coded video program to the available data space to achieve a high average picture quality. The target bitrate to be achieved is calculated from the available data space and the time to be recorded. The actual bitrate is monitored and if it deviates from the target bitrate the compression settings are adjusted. In the event of video material with a lot of activity, the applied settings will often result in a higher actual bitrate than the target bitrate. The compression settings will then be adjusted. However in the first part of the recording time with such video material a more than proportional amount of data space will be filled. Therefore an adjustment of the target bitrate during the further recording time will be required.
It is well known to provide structures to perform functions in a controller by programming the controller and to copy structures from the memory of one controller into the memory of another controller to program the other controller. Thus, a programmed controllers illustrated herein provide apparatus for programming another controller.
It is an object of the invention to provide apparatus for directly converting a supplied signal into compressed data, so that the total quantity of compressed data of a program that has a predefined duration fills as much as possible the available data space while the (subjective) quality during the program is substantially constant after reconstruction by decompression of the compressed data.
For this purpose, the encoding device according to the invention is characterized in that the system controller is arranged for setting the compression unit depending on a program complexity of the actual program.
For this purpose, a recording device according to the invention includes such an encoding device.
The method according to the invention is characterized in that the compression process is set depending on a program complexity of the actual program.
By implementing these measures the actual bitrate will be vary less throughout the recording time. This is advantageous in that the subjective quality for the user will be more constant. By taking the complexity into account it will be prevented that, when encoding a complex program, the first part uses more than half of the available bits, while the second part needs to be compressed heavily to fit in the remaining data space; while for less than average complex material the opposite (a first part unnecessarily compressed and the second part having abundant space available) is prevented. A further advantage is that, the measures avoid the last minutes of a program being heavily compressed because the available data space has almost been fully used, because more compressed data than average is generated for a selected quality for the respective program.
A further embodiment for the encoding device according to the invention is characterized in that the system controller is arranged for determining the program complexity depending on an actual bit rate during a previously encoded part of the program. This is advantageous in that the complexity of the program is determined from the actual program characteristics during an early part of the recording time and is used subsequently.
A further embodiment for the encoding device according to the invention is characterized in that system controller is arranged for establishing the program complexity depending on peaks and valleys or variation of the actual bit rate during a previously encoded part of the program. This is advantageous in that they complexity is determined not only from the actual average bitrate, but also from further properties, which allows a more accurate prediction of the compression settings.
A further embodiment for the encoding device according to the invention is characterized in that the system controller is arranged for establishing the program complexity depending on a program type. This is advantageous in that the influencing of the bit rate is effected from the start of the recording time, as the average complexity of such a program is known from the program type.
A further embodiment for the encoding device according to the invention is characterized in that the system controller is arranged for determining the duration depending on an expected duration of the program and a margin for levelling peaks in the bit rate in a last part of the program and/or for the program overrunning its time. By adding a margin to the expected duration and using this total duration for influencing the bit rate, space is available for storing more data than expected. This is advantageous in that, for example, in a complex final scene in a video program, the bit rate need not be restricted unproportionally and in that sufficient data space remains available even if the program slightly overruns its time.
Those skilled in the art will understand the invention and additional objects and advantages of the invention by studying the description of preferred embodiments below with reference to the following drawings which illustrate the features of the appended claims.